System and method for generating and detecting the identifier sequence of the  bandwidth-limited transmitter

ABSTRACT

A system and method for generating and detecting identifier sequence of a bandwidth-limited transmitter are disclosed, comprising an identifier sequence generating portion and a detection portion. The identifier sequence generating portion comprises: generating a frequency-domain random sequence; generating a frequency-domain orthogonal sequence; performing frequency-domain truncation; performing frequency-time transformation; and performing cycle extension. The identifier sequence receiving portion comprises: truncating the time-domain for the received signal; performing time-frequency domain transformation to obtain a frequency-domain signal; generating frequency-domain random sequence; generating a frequency-domain orthogonal sequence; correlating the frequency-domain orthogonal sequence with the frequency-domain signal de-scrambled by the frequency-domain random sequence; and detecting an output from a frequency-domain correlator by a threshold detecting device and determining the transmitter identifier sequence. The random sequence bandwidth generated by the system and the method of the present invention can be configured flexibly according to transmission bandwidth requirement, and the sequence may be arbitrarily allocated at the power of each frequency point inside the bandwidth. The present invention may be widely applied to multimedia broadcasting, terrestrial radio broadcasting, cable broadcasting and the like.

TECHNICAL FIELD

The present invention relates to digital information transmissiontechnology, and more particularly, to generation and detection ofbandwidth-limited identifier sequence in an OFDM digital broadcastsystem.

BACKGROUND

Besides broad coverage and large program capacity, the most excellentcharacteristic of digital broadcast is its broadcast capability whichcan be point-to-points and point-to-face, and the cost of broadcastinginformation is not related to quantity of users. Thus, as an importantcomponent of information communication industry, the digital broadcastplays an important role in the construction of national informationinfrastructure and realization of normal service and nationalinformation security strategy.

In digital broadcasting service, the entire country is normally dividedinto districts, which also can be divided into multi-levels, eachdistrict can be configured with a plurality of broadcasting signaltransmitters. To facilitate the receiving end obtaining the source ofthe received signal, the transmitter has to be identified in thetransmitting signals. And these identified signals are generallyrepresented in form of pseudo-random sequences. Further, to facilitatedetecting the identifier signals of the transmitter by the receiver, itis preferable that these identifier signals have orthogonal properties.

In an OFDM system, a sampling rate is normally higher than a bandwidthof the system, for example, a bandwidth of 8 MHz with a sampling rate of10 MHz. However, generally, a random sequence generating devicegenerates a random sequence on the time-domain directly. For example,after a m-sequence generator generates a m-sequence x(n), a time-domainrandom sequence is generated by BPSK mapping. When the sampling rate is10 MHz, the bandwidth of the sequence is at least 10 MHz, which mayexceed the limit of the system bandwidth.

SUMMARY OF INVENTION

As described above, in a digital broadcasting system based on OFDM, anovel method for generating random sequences is needed.

Therefore, the present invention provides a system for generating anddetecting an identifier sequence of a bandwidth-limited transmitter,comprising an identifier sequence generating portion and an identifiersequence detecting portion.

The identifier sequence generating portion comprises: a frequency-domainrandom sequence generating device for generating a frequency-domainrandom sequence; a frequency-domain orthogonal sequence generatingdevice for generating a frequency-domain orthogonal sequence; afrequency-domain truncating device for frequency-domain truncating thefrequency-domain orthogonal sequence scrambled by the frequency-domainrandom sequence; a frequency-time transforming device for performingfrequency-time domain transformation of the truncated frequency-domainsequence; and a periodic extending device for performing periodicextension of the signal transformed into time-domain.

The identifier sequence receiving portion comprises: a time-domaintruncating device for performing time-domain truncating of the receivedsignal to obtain a time-domain signal carrying transmitter identifyinginformation; a time-frequency domain transforming device for performingtime-frequency domain transformation of the truncated time-domain signalto obtain frequency-domain signal; a frequency-domain random sequencegenerating device for generating a frequency-domain random sequence; afrequency-domain orthogonal sequence generating device for generating afrequency-domain orthogonal sequence; a frequency-domain correlator forcorrelating the frequency-domain orthogonal sequence with thefrequency-domain signal de-scrambled by the frequency-domain randomsequence; and a threshold detecting device for detecting output of thefrequency-domain correlator and determining the transmitter to which theidentifier sequence belongs.

The present invention also provides another method of generating anddetecting an identifier sequence of a bandwidth-limited transmitter,comprising a method of generating the identifier sequence and a methodof detecting the identifier sequence.

The method of generating the identifier sequence comprises: generating afrequency-domain random sequence by a frequency-domain random sequencegenerating device; generating a frequency-domain orthogonal sequence bya frequency-domain orthogonal sequence generating device; performingfrequency-domain truncation to the frequency-domain orthogonal sequencescrambled by the frequency-domain random sequence with afrequency-domain truncating device; performing frequency-time domaintransformation to the truncated frequency-domain sequence with afrequency-time transforming device; and performing periodic extension tothe time-domain signal with a periodic extending device.

The identifier sequence receiving portion comprises: performingtime-domain truncation to the received signal with a time-domaintruncating device; performing time-frequency domain transformation tothe truncated time-domain signal with a time-frequency domaintransforming device to obtain a frequency-domain signal; generating afrequency-domain random sequence with the frequency-domain randomsequence generating device; generating frequency-domain orthogonalsequence with the frequency-domain orthogonal sequence generatingdevice; correlating the frequency-domain orthogonal sequence with thefrequency-domain signal de-scrambled by the frequency-domain randomsequence with a frequency-domain correlator; and detecting the output ofthe frequency-domain correlator with a threshold detecting device anddetermining the transmitter identifier sequence.

The present invention was realized by time-frequency transformation andscrambling and de-scrambling of the orthogonal sequence, includingfollowing features:

The bandwidth of the random sequence is equal or less than the systembandwidth, which may be flexibly configured based on transmissionbandwidth;

The power of the sequence in each frequency point of the band can bearbitrarily allocated;

The orthogonality and pseudo-randomness of the transmitter identifiersequence can be insured which may facilitate the detection of thereceiver; and

The identifier sequence generated by the present invention can beflexibly applied to situations of multi-level divided districts.

The present invention can be widely applied to multimedia broadcasting,terrestrial radio broadcasting, cable broadcasting and the like.

BRIEF DESCRIPTION OF DRAWINGS

The present invention is described but not limited in conjunction withthe embodiments shown in the drawings throughout which the similarreference signs represent the similar elements, in which:

FIG. 1 shows a flow chart of generating a bandwidth-limited transmitteridentifier signal according to some embodiments of the presentinvention;

FIG. 2 shows a flow chart of detecting the transmitter identifier signalat the receiving end according to some embodiments of the presentinvention;

FIG. 3 shows a beacon structure of a multimedia broadcasting systemaccording to some embodiments of the present invention;

FIG. 4 shows a schematic view of a bandwidth-limited random signalgenerator in the multimedia broadcasting system according to someembodiments of the present invention;

FIG. 5 shows a schematic view of a shift register for generating acomplex-m sequence according to some embodiments of the presentinvention; and

FIG. 6 shows a flow chart for detecting the identifier sequence at thereceiving end according some embodiments of to the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

The preferred embodiments of the present invention will be described indetail with reference to accompanying figures.

FIG. 1 shows a flow chart of generating a bandwidth-limited transmitteridentifier signal according to some embodiments of the presentinvention. As shown in the figure, the process includes five parts,i.e., generating frequency-domain random sequence, generatingfrequency-domain orthogonal sequence, frequency-domain truncating,frequency-time domain transforming and time-domain periodic extension.

The frequency-domain random sequence generator generates afrequency-domain complex random sequence at the receiving end:

X(n)=A(n)·m(n),0≦n≦N−1

The frequency-domain orthogonal sequence generator generates afrequency-domain complex orthogonal sequence:

W(n),0≦n≦N−1

Wherein N is the length of the frequency-domain sequence, m(n) is arandom sequence generated in a specific manner based on systembandwidth, A(n) is an amplitude gain of the random sequence at eachfrequency point, which is selected based on power distributionrequirement in the bandwidth. The complex orthogonal sequence may be aWalsh sequence, a Hadamard sequence or an orthogonal sequence generatedin other manner. The complex orthogonal sequence is truncated based onsystem requirement after frequency-domain scrambled by the complexrandom sequence, and a time-domain transformer transforms the truncatedfrequency-domain identifier sequence to the time-domain. Further, basedon the system requirement, the time-domain sequence generated byfrequency-time domain transformation is subjected to periodic extension.

FIG. 2 shows a flow chart of detecting the transmitter identifier signalat the receiving end according to some embodiments of the presentinvention. As shown in FIG. 2, it comprises time-domain truncating,time-frequency domain transforming, frequency-domain random sequencegenerating, frequency-domain orthogonal sequence generating, acorrelator and threshold detecting.

The receiving end obtains the time-domain identifier sequence of thetransmitter by time-domain truncation, and the time-domain identifiersequence is transformed into frequency-domain by time-frequency domaintransformation, after frequency-domain de-scrambling and relatedcalculation with the corresponding identifier sequence, and finally, therelated result is compared with a threshold to determine the source ofthe received signal.

In a multimedia broadcasting system with a sampling rate of 10 MHz and asystem bandwidth of 8 MHz, the bandwidth-limited random sequence isfunctioned as a beacon. FIG. 3 shows a beacon structure of themultimedia broadcasting system according to some embodiment of thepresent invention. As shown in FIG. 3, the beacon includes a transmitteridentifier sequence with 191 points, and the identifier sequence can beperiodically extended to 280 points with 256-point IFFT in time-domain.

FIG. 4 shows a schematic view of a bandwidth-limited random signalgenerator in the multimedia broadcasting system according to someembodiments of the present invention. The frequency-domain truncatedsequence is obtained by scrambling the orthogonal sequence with them-sequence, then the sequence undertakes Fourier transformation togenerate a bandwidth-limited random sequence having a bandwidth of 8Mwithout DC component, then it is subjected to periodic extension toobtain the transmitter identifier sequence. More detained description isas follows.

In the complex m-sequence generator 1, the m-sequence M(n) is generatedby a shift register having a polynomial of x8+x7+x6+x+1 where 0≦n≦254.The structure of the shift register is shown in FIG. 5, with an initialstate of 0000 0001.

Then, the m-sequence is mapped into the complex m-sequence:

${K(n)} = \left\{ \begin{matrix}{{1 + {0j}},} & {{M(n)} = 0} \\{{{- 1} + {0j}},} & {{M(n)} = 1}\end{matrix} \right.$

The complex m-sequence generator may be SSRG structure, MSRG structureor Gold structure.

A gain function generator 2 can generates a gain function based on thesignal frequency-domain characteristics of power average distribution inthe passband:

${A(n)} = \left\{ \begin{matrix}{1,} & {1 \leq n \leq {95\mspace{14mu} {or}\mspace{14mu} 160} \leq n \leq 255} \\{anywalue} & {{other}\mspace{14mu} {range}}\end{matrix} \right.$

The positioned m-sequence is multiplied with the gain function by amultiplier 3, and the frequency-domain sequence before transformation isobtained:

X(n)=P(n)*A(n),0≦m≦255

256 Walsh sequences W(n) with lengths of 256 are generated by a Walshsequence generator 4, and the obtained Walsh sequences are alsotransformed into a complex frequency-domain sequence W(n):

${W(n)} = \left\{ \begin{matrix}{{1 + {0 \cdot j}},} & {{w(n)} = 0} \\{{{- 1} + {0 \cdot j}},} & {{w(n)} = 1}\end{matrix} \right.$

The output of the multiplier X(n) is multiplied with the Walsh sequenceW(n) to obtain a complex symbol sequence having a length of 256. Asequence truncating device 5 extracts the 66^(th) to 256^(th) elementsin the complex symbol sequence based on system requirements to obtain afrequency-domain complex random sequence S(n) having a length of 191.

Based on the requirement of a 8M signal bandwidth without DC component,a sequence locator 6 positions the m-sequence at an appropriate place inthe frequency domain before domain transformation to obtain a 256-pointfrequency-domain random sequence:

${P(n)} = \left\{ \begin{matrix}{0,} & {n = 0} \\{{S\left( {n - 1} \right)},} & {1 \leq n \leq 95} \\{0,} & {96 \leq n \leq 159} \\{{S\left( {n - 65} \right)},} & {160 \leq n \leq 255}\end{matrix} \right.$

The P(n) is transformed into time-domain by a Fourier transformer 7 toobtain a time-domain random sequence:

${{p(k)} = {{{FFT}\left\lbrack {P(n)} \right\rbrack} = {\frac{1}{16}{\sum\limits_{n = 0}^{255}{{P(n)}^{{j2\pi}\; {{nk}/256}}}}}}},{0 \leq k \leq 255}$

Because the system requires the transmitter identifier sequence having280 points in the time domain whereas the 256-point time-frequencydomain transformation is performed herein, the 256-point time-domainsequence is periodic extended to 280 points by a period extending device8.

Through the above steps, 256 pseudo-random transmitter identifiersequences are obtained. If secondary division is needed, i.e., the wholecountry has to be divided into 128 districts, each district may have 128transmitters at maximum. And the 256 transmitter identifier sequencesmay be arbitrarily divided into two sets, each set containing 128identifier sequences. The sequences in one set are allocated to 128different districts, and the sequences in the other set are allocated tothe transmitters in each district. The identifier of the district may betransmitted in even time-slots and the identifier of the transmitteritself can be transmitted in odd time-slots, or vice versa.

If it is divided into 4 levels, the whole country is divided into 64districts, each district is also divided into 64 primary sub-districts,and each primary sub-district is divided into 64 secondarysub-districts, and each secondary sub-districts may have 64transmitters. And the 256 identifier sequences are divided into 4sub-sets, each sub-set contains 64 different identifier sequences. The64 sequences in the first sub-set are allocated to the 64 sub-districtsin the uppermost layer, the 64 sequences in the second sub-set areallocated to the 64 primary sub-districts in each district, the 64sequences in the 3rd sub-set are allocated to 64 secondary sub-districtsin each primary sub-district, the 64 sequences in the 4^(th) sub-set areallocated to 64 transmitters in each secondary sub-district. Each levelof sub-districts and the identifier sequence of the transmitter can betransmitted in turn in the adjacent 4 time slots.

If divided in other manner, the identifier sequences obtained can beflexibly allocated based on the above method.

To obtain the source of the received signal at the receiving end, it isnecessary for the receiver to detect by the transmitter identifierinformation carried in the receiving signal.

The transmitter identifier sequence detecting device at the receivingsignal is shown in FIG. 6, which is described in detail in thefollowing.

The time-domain truncating device 1 truncates data sequence y(k) with asymbol length of 256 in a corresponding position in the received datar(k), 0≦k≦255.

The Fourier transformer 2 transforms the identifier sequence fromtime-domain to frequency-domain, and obtains the followingfrequency-domain sequence:

${{Y(n)} = {{{FFT}\left\lbrack {y(k)} \right\rbrack} = {\frac{1}{16}{\sum\limits_{k = 0}^{255}{{y(k)}^{{- {j2\pi}}\; {{nk}/256}}}}}}},{0 \leq n \leq 255}$

The complex m-sequence generator 3, the gain function generator 4 andthe multiplier 5 have the same function as the complex m-sequencegenerator 1, the gain function generator 2 and the multiplier 3 in FIG.4.

The output of the multiplier is the complex symbol sequence X′ (n) witha length of 256. The m-sequence truncating device 6 extracts the 66^(th)to 256^(th) elements of the complex symbol sequence for the lengthcoinciding with the receiving end, thus obtaining a frequency-domaincomplex random sequence S′(n) having a length of 191 to de-scramble inthe frequency-domain.

The Walsh sequence generator 7 has the same function as the Walshsequence generator 4 in FIG. 4.

The Walsh sequence generator generates a complex symbol sequence W′(n)having a length of 256. The Walsh sequence truncating device 8 extractsthe 66^(th) to 256^(th) elements of the complex symbol sequence for thelength coinciding with the receiving end, thus obtaining afrequency-domain complex random sequence Z(n) having a length of 191 tode-scramble in the frequency-domain.

The frequency-domain correlator 9 correlates the Y′(n) obtained afterde-scrambling with the Walsh sequence Z(n), and obtains:

${R_{Y^{\prime}Z}(\tau)} = {\sum\limits_{n = 0}^{190}{{Y^{\prime}(n)} \cdot {Z\left( {n - \tau} \right)}}}$

Finally, the threshold detector compares the correlating valueR_(Y′Z)(0)) with a predetermined threshold value Threshold. IfR_(Y′Z)(0)≧Threshold, the Walsh sequence generated by the Walsh sequencegenerator is an identifier sequence of a certain transmitter at thetime, otherwise, not. The threshold value Threshold may be predeterminedbased on actual system requirement.

Although the present invention is described in conjunction with theexampls and embodiments, the present invention is not intended to belimited thereto. On the contrary, the present invention obviously coversthe various modifications and may equivalences, which are all enclosedin the scope of the following claims.

1. A system for generating and detecting an identifier sequence of abandwidth-limited transmitter, comprising an identifier sequencegenerating portion and an identifier sequence detecting portion,wherein, the identifier sequence generating portion comprises: afrequency-domain random sequence generating device for generating afrequency-domain random sequence; a frequency-domain orthogonal sequencegenerating device for generating a frequency-domain orthogonal sequence;a frequency-domain truncating device for frequency-domain truncating thefrequency-domain orthogonal sequence scrambled by the frequency-domainrandom sequence; a frequency-time transforming device for performingfrequency-time domain transformation of the truncated frequency-domainsequence; a periodic extending device for performing periodic extensionof the signal transformed into time-domain; the identifier sequencereceiving portion comprises: a time-domain truncating device forperforming time-domain truncation of the received signal; atime-frequency domain transforming device for performing time-frequencydomain transformation of the truncated time-domain signal to obtainfrequency-domain signal; a frequency-domain random sequence generatingdevice for generating a frequency-domain random sequence; afrequency-domain orthogonal sequence generating device for generating afrequency-domain orthogonal sequence; a frequency-domain correlator forcorrelating the frequency-domain orthogonal sequence with thefrequency-domain signal de-scrambled by the frequency-domain randomsequence; and a threshold detecting device for detecting output of thefrequency-domain correlator and determining the transmitter to which theidentifier sequence belongs.
 2. A method of generating and detecting anidentifier sequence of a bandwidth-limited transmitter, comprising amethod of generating the identifier sequence and a method of detectingthe identifier sequence, wherein the method of generating the identifiersequence comprises: generating a frequency-domain random sequence by afrequency-domain random sequence generating device; generating afrequency-domain orthogonal sequence by a frequency-domain orthogonalsequence generating device; performing frequency-domain truncation tothe frequency-domain orthogonal sequence scrambled by thefrequency-domain random sequence with a frequency-domain truncatingdevice; performing frequency-time domain transformation to the truncatedfrequency-domain sequence with a frequency-time transforming device toobtain a time-domain signal; performing periodic extension to thetime-domain signal with a periodic extending device; the method ofdetecting identifier sequence comprises: performing time-domaintruncation to the received signal with a time-domain truncating device;performing time-frequency domain transformation to the truncatedtime-domain signal with a time-frequency domain transforming device toobtain a frequency-domain signal; generating a frequency-domain randomsequence by the frequency-domain random sequence generating device;generating frequency-domain orthogonal sequence by the frequency-domainorthogonal sequence generating device; correlating the frequency-domainorthogonal sequence with the frequency-domain signal de-scrambled by thefrequency-domain random sequence with a frequency-domain correlator; anddetecting the output of the frequency-domain correlator with a thresholddetecting device and determining the transmitter identifier sequence. 3.The method according to claim 2, wherein the frequency-domain randomsequence generated by the frequency-domain random sequence generator isX(n)=A(n)·m(n), 0≦n≦N−1, in which m(n) is a random sequence which isgenerated based on the system bandwidth, A(n) is an amplitude gain ofthe random sequence at each frequency point, which is selected based onpower distribution in the bandwidth of the system.